In some passenger transport vehicles, such as air planes, dimmable light units have started to become common place in the interior of the cabin. These dimmable light units are for example used for the general illumination of the main cabin or for illuminating the wash cabins or for other illumination purposes. In order to make the light units dimmable, pulse width modulation (PWM) is commonly used to drive the light sources. The underlying principle of dimming by pulse width modulation is as follows. The current provided to the light sources is switched on/off at a high frequency which switching cannot be perceived by the human eye. The duty cycle of such pulse width modulation is the portion of the total time that is dedicated to the on-state of the light source. A longer portion of the on-state is perceived by the human eye as a higher light intensity. Consequently, the duty cycle determines the light intensity perceived by the human eye, i.e. the degree of dimming of the light unit.
The switching of the light source drive current results in a non-continuous load for the electricity network, to which the light unit is connected. The switching creates undesired influences on the electricity network. In other words, the switching has an undesired “backwards” effect on the electricity network. An example for such an undesired effect is a current amplitude modulation in the electricity network. This makes an efficient operation of the electricity network difficult. Moreover, the light unit itself has to be provided with circuit elements that can handle such non-continuous current flow.
Accordingly, it would be beneficial to provide a dimmable light unit that poses less of a strain on the electricity network that it is connected to. Further, it would be beneficial to provide a method of replacing existing light units with such improved dimmable light units.